Drying equipment

ABSTRACT

In the vapour phase drying of the insulation of electrical transformers, the vapour is generated by a permeable element heater temporarily positioned in the interior of the transformer housing and to which is fed both the liquid to be vaporized and heating current for the electroresistive element.

United States Patent Kusay Sept. 9, 1975 [i DRYING EQUIPMENT 3205589 9/1965 Fles ct al. 34 32 154L696 ll/l970 Dunn. Jr. 1. 34/27 [76] Inventor Roland Gregor Paul Kusay, 6 3,688,083 8/l972 Rice et al 219/275 Batterys Cross, Blechmgley, England FOREIGN PATENTS OR APPLICATIONS [22] Filed, Nov 20 1973 9l4,390 l/l963 United Kingdom 34/36 [2]] Appl' 417558 Primary ExaminerCarroll B. Dority, Jr.

Assistant Examiner-Larry I. Schwartz 30 Foreign A fi gi priority m Attorney, A ent, or Firm-Dennison, Dennison,

Nov. 22 1972 United Kingdom 1. 53957 72 Townshend Mesemle 52 us. c1. 34/32; 34/36; 34/76; 7 ABSTRACT [51] Int Cl 1 :4533 In the vapour phase drying of the insulation of electri- [58] Fieid 34/27 32 cal transformers, the vapour is generated by a permea- 37 ble clement heater temporarily positioned in the interior of the transformer housing and to which is fed [56] References Cited both the liquid to be vaporized and heating current for the electroresistive element. UNITED STATES PATENTS 2,348,465 5/1944 Geiringcr 34/15 4 Claims, 1 Drawing Figlm3 DRYING EQUIPMENT This invention relates to the drying of equipment, and particularly to the drying of insulated electrical equipment of which the insulation contains sorbed water vapour which reduces the dielectric strength of the insulation.

It is known to dry such equipment by a process known as vapour phase drying, in which process heat is transferred to the insulation by the heat released when a vapour of a suitable liquid condenses on the insulation. This has the considerable advantages that the vapour is highly mobile, so that it is able to condense on otherwise inaccessible surfaces, and that those parts of the insulation which contain most moisture remain relatively colder than the surrounding drier insulation, so that there is a preferential condensation of vapour on such wetter" parts.

Vapour phase drying is normally carried out in conjunction with the selective application of vacuum, so that the condensate is continually drawn off and recirculated after it has been separated from the water vapour which is drawn off with it.

The vapour is normally supplied by a boiler or other vaporiser positioned externally of the container of the transformer or other equipment being dried, and connected to it by large-diameter lagged trunking. This trunking necessitates the container being provided with a large entry port which lowers the theoretical strength of the container and so is a point of weakness.

The present invention aims at providing a method of vapour phase drying electrical or other equipment housed in the container, in which the vapour is generated within the interior of the container so that only small access ports need by provided in the walls of the container.

Accordingly the present invention provides a method of drying electrical or other equipment which is as claimed in the appended claims.

The present invention will now be described by way of example with reference to the accompanying drawing, which is a diagrammatic view of an electrical transformer having its windings and insulation dried in accordance with the present invention.

The accompanying drawing shows a container 2 housing an electrical transformer 4 of which the shape is indicated only diagrammatically. Secured to one end of the container is a cover plate 6 having in it a port 10 of size large enough to permit the body of an electrical heater 12 of the permeable element type being introduced into the interior of container 2. Integral with the heater 12 is a mounting flange 14 which is secured to cover plate 6, in a vacuum-tight manner, by any suitable means, such as bolts (not shown). The actual constructional details of the heater 12 are irrelevant, although it can take the form disclosed in our copending application 30147/71. now US. Pat. Nov 3,781,518.

The illustrated heater 12 comprises a hollow cylindrical body 16 of a permeable, electroresistive material which extends between two terminals 18 and 20 which are adapted to be connected to opposite poles of a supply of electric current 21. The two poles are connected to that portion 22 of the heater which projects upwardly from flange 14. Liquid to be vaporized flows into the heater through tubular conduit 24.

In operation a flow of White spirit, kerosene or other light oil to be vaporised is started immediately before electric current is passed longitudinally through body 16. The electric current is of amplitude sufficient to generate sufficient Joule heat to vaporize substantially all of the liquid entering the heater. This is to ensure that the body 16 is not destroyed by being heated while no liquid is being passed through it. This results in liquid dropping directly into the interior of container 2, but after a time the amount of liquid is reduced as an increasing percentage of it is vaporised before the liquid reaches the exterior surfaces of body 16. Under some operating conditions the flow of liquid is always slightly greater than the portion thereof which is vaporised, so that there is a dribble ofliquid from the heater. This is to ensure that the element is always adequately cooled, because the presence of this dribble of oil shows that the external temperature of the element is not excessive.

Vapour issuing from body 16 tends to fill the whole of the interior of container 2 and to come into contact with every part of the surface area of the electrical equipment 4. Those parts of the equipment which are relatively-dry tend to warm up quickly as the heat of condensation is transferred to them. With the increase of temperature there is a reduction in the tendency of vapour to condense on them.

Those parts of the equipment 4 which are relatively wet appear to the vapour to remain cold despite the transfer of heat to them by the condensing vapour. This is because the heat of condensation is transferred to the sorbed water vapour and becomes converted into heat of vaporisation without appreciably raising the temperature of the insulation itself. This means that, as long as the insulation contains sorbed water vapour, it remains cold and therefore there is a tendency for the vapour to condense preferentially on such wetter parts of the equipment. The overall effect is for the vapour to transfer heat to those parts of the equipment which most need it. Because of the high mobility of the vapour, this occurs despite the relative inaccessibility of parts of the equipment, so that the equipment tends as a whole to have its wetter parts dried out at a faster rate than its drier parts, which is approaching the ideal solution.

During the drying process the vacuum is supplied by vacuum pump 9 to the interior of container 2 so as to withdraw from the container both condensate and de sorbed water vapour. The condensate is condensed in condenser 26 and the water vapour is condensed in condenser 28. The condensate and any liquid from the bottom of container 2 flow into reservoir 23 and are recycled to the heater by pump 30. The rate of pumping of vacuum pump 9 can be controlled during the drying process so that the degree of vacuum evaporation can be correlated with the rate at which water vapour is evolved to keep the two parameters at an optimum level leading to the water content of the insulation being reduced to the desired maximum level in an acceptably short time, which is appreciably less than the time needed to dry electrical insulation by alternate methods.

Because the light oil to be vaporised is introduced into the interior of container 2 while in its liquid form, the size of the port 10 is governed more by the size of heater [2 than by the size of the oil conduit 24. Even then, the size of port 10 is appreciably less than that needed to accommodate the trunking necessary to allow an equivalent amount of vapour to enter container 2 from a remote boiler or vaporiser. As heat loses in the associated trunking are also avoided, the efficiency of the drying process is improved, as well as the mechanical strength of the container.

I claim:

1. A method of drying water from electrical equipment by transferring heat to it by the condensation on it of saturated or superheated vapour of a liquid of a member of the class consisting of white spirit, light oil and kerosene, including the steps of positioning an electrical heater having a permeable hollow cylindrical body of electroresistive material within the interior of a vacuum-tight container housing the equipment to be dried; supplying liquid to the heater; forcing said liquid through the body while passing electrical current therethrough of amplitude sufficient to generate sufficient Joule heat to vaporise substantially all the liquid entering the heater and continually evacuating the interior of the container and removing both the liquid vapour and desorbed water vapour.

2. A drying method as claimed in claim 1, including the further steps of condensing the liquid vapour and desorbed water vapour removed from the container, and of returning the liquid to the heater.

3. A drying method as claimed in claim 1, in which the amplitude of the electric current in the heater is such that some unvaporized liquid will pass from the heater.

4. A drying method as claimed in claim 1, in which the heater is in the form of a hollow cylinder into the interior of which the liquid is supplied. 

1. A method of drying water from elecTrical equipment by transferring heat to it by the condensation on it of saturated or superheated vapour of a liquid of a member of the class consisting of white spirit, light oil and kerosene, including the steps of positioning an electrical heater having a permeable hollow cylindrical body of electroresistive material within the interior of a vacuum-tight container housing the equipment to be dried; supplying liquid to the heater; forcing said liquid through the body while passing electrical current therethrough of amplitude sufficient to generate sufficient Joule heat to vaporise substantially all the liquid entering the heater and continually evacuating the interior of the container and removing both the liquid vapour and desorbed water vapour.
 2. A drying method as claimed in claim 1, including the further steps of condensing the liquid vapour and desorbed water vapour removed from the container, and of returning the liquid to the heater.
 3. A drying method as claimed in claim 1, in which the amplitude of the electric current in the heater is such that some unvaporized liquid will pass from the heater.
 4. A drying method as claimed in claim 1, in which the heater is in the form of a hollow cylinder into the interior of which the liquid is supplied. 